Photodynamic therapy involves the administration of a photosensitizing compound and subsequent irradiation with light of tissue to which the photosensitizing compound has selectively homed. The target tissue containing a sufficiently high concentration of the photosensitizing compound selectively absorbs the light which results in impairment or destruction of the immediately surrounding cells. U.S. Pat. No. 5,095,030 describes procedures wherein photosensitizing compounds are administered to animals which are subsequently irradiated using external light sources. For example, Example 5 of this patent describes subcutaneous injection of mice with P815 tumor cells which grow into a palpable tumor. Photosensitizing compounds are then injected, and after the animals are maintained in the dark for three hours, their tumors were exposed to a strong light. The survival rates of the treated animals were improved over untreated controls. Similarly, Example 8 of that patent describes use of a rhabdomyosarcoma system in mice with a similar protocol. Thus, these examples are directed to the treatment of localized solid tumors where the externally applied light is trained on the tumor. In these instances, the target tissue is not contained in the bloodstream where the treatment must avoid damage to the blood vessels and non-targeted blood cells.
U.S. Pat. No. 4,960,408 discloses the treatment of contents of the bloodstream (HIV virus and infected T-cells) by photopheresis. In this technique the patient's blood is routed through an extracorporeal apparatus in which the white cell fraction of the blood is exposed to ultraviolet light before the white cells are returned to the patient.
Benzoporphyrin derivatives (BPD), in combination with red light (400-900 nm), have been reported to be effective in eliminating both free viruses and virally infected cells from spiked blood products and from whole blood obtained from viremic cats. Red blood cells appeared viable after the virucidal treatment. North etal. Blood Cells 18:129-40, 1992.
BPD also has a demonstrated higher affinity for tumor tissue, including leukemic cells, than for normal non-malignant cells. Jamieson etal., Leukemia Res. 14:209-19, 1990.
U.S. Pat. No. 5,095,030, issued 10 Mar. 1992, which is incorporated herein in its entirety by reference, discloses and claims various wavelength-specific cytotoxic agents which are generically described as "green porphyrins." These compounds are porphyrin derivatives which are modified by a Diels Alder reaction effectively to shift the wave length of absorption to a longer wavelength. This results in some favorable properties as compared to, for example, hematoporphyrin derivative when these compounds are employed in photodynamic therapy generally. As described in this patent, these cytotoxic agents, when administered systemically, "home" to unwanted cells, in particular to tumor cells or pathogenic viruses and subsequent irradiation with light absorbed in by these compounds causes them to transition in such a way as to effect cytotoxicity.
Pending application Ser. No. 07/832,542, filed Feb. 5, 1992, discloses the preparation of liposomes of porphyrin photosensitizers.